1. Field of the Invention
The invention relates to a conveyor mat for conveying products in a conveying direction between at least two divert wheels, comprising a number of rows of side-by-side modules succeeding each other in the conveying direction and extending transversely to the conveying direction, which modules, viewed in conveying direction, each have their front and rear sides provided with hinge loops, the hinge loops of said successive rows of modules cooperating and being coupled by means of hinge pins extending transversely to the conveying direction, such that the top faces of the modules together constitute a conveying face, into which conveyor mat a number of guide modules are incorporated which have their bottom side provided with guide members for cooperation with at least one guide provided on a conveying track.
2. Description of Related Art
Such conveyor mats are known and are used for conveying all types of products in a large number of different environments. The conveyor mat often constitutes an endless belt traveling around between two groups of divert wheels, the conveying face being supported by a conveying track. Usually, the conveyor mat is built up from a large number of plastic modules which are each manufactured by injection molding. During manufacture of the modules, a certain measure of difference between the dimensions of the plastic modules must be allowed for, due to differences in shrinkage or differences between the different mold cavities present in a mold for the purpose of injection molding. In addition, the loop thickness of a module is always less than the space between two loops, to allow the modules to interfit, as a result of which these modules already have a certain play relative to each other during assembly of the conveyor mat. During use, this play may even increase due to wear and stretching of the modules.
Because of this play, the modules of the conveyor mat can slide relative to each other. This inter alia results in a possible width variation of the conveyor mat due to the modules of a row sliding in and out transversely to the conveying direction. Further, because of this, the rows of modules of the conveyor mat may slide back and forth relative to the conveying track, between a position in which either one outer module or the other outer module of a row is located adjacent a lateral edge of the conveying track. In the worst case, this may already cause a width variation of 1%.
In practice, this causes various problems. For instance, the lateral edge of the conveyor mat may rub along a lateral edge of the conveying track, which may lead to wear of and damage to the modules located adjacent the edges of the conveyor mat. This increases the chance of breakage of the conveyor mat. The conveyor mat may be entirely located along one side of the conveying track or zigzag along both lateral edges of the conveying track. Another problem caused by the play between the modules and the rows of the conveyor mat sliding back and forth, is that in practice, the width over which the conveyor mat can be loaded with products must be chosen to be less than the nominal width of the conveyor mat, while the conveying track must be chosen to the greater than the nominal width of the conveyor mat. In particular in the case of long conveying tracks, this may result in high additional costs and substantial loss of space.
To reduce the above problems, it has already been proposed to incorporate into a conveyor mat, adjacent its two lateral edges, modules whose bottom sides are provided with guide projections, each for cooperating with a wear strip extending adjacent a lateral edge of the conveying track. Such a conveyor mat is known from U.S. Pat. No. 5,372,248. One guide projection prevents movement of the conveyor mat in one transverse direction, while the other guide projection prevents movement in the opposite transverse direction. The distance between the guides is selected so that during placement of the conveyor mat on the conveying track, the play in width direction is precisely removed.
In particular, U.S. Pat. No. 5,327,248 describes a flexible conveyor mat whose lateral sides comprise guide modules designed as end modules. The guide modules are incorporated into the conveyor mat in such a manner that the guide members thereof form two guide tracks, each extending adjacent a lateral side of the conveyor mat. The guide members comprise a substantially hook-shaped part which, in a bend, can engage below a guide provided on a guide track, to prevent the conveyor mat from moving up during travel around a bend. The guide members further comprise a substantially block-shaped guide projection which, relative to the hook-shaped part, is located more towards the center of the conveyor mat. The guide projection is intended to cooperate with the guide, in particular when traveling around a bend. One guide projection impedes movement of the conveyor mat in one transverse direction, while the other guide projection prevents movement in the opposite transverse direction.
However, when the play transverse to the conveying direction becomes too great, the effect of such construction becomes lost. In particular, due to the increased play between the wear strip and the guide projection, movement in transverse direction will no longer be sufficiently prevented. In addition, because of the difference in dimensions of the modules, the distance between the guide members of the guide modules may vary per row. This is particularly the case when the rows of the conveyor mat comprise a large number of modules, as in a wide conveyor mat. Further, such a construction cannot be used when the conveyor mat is exposed to substantial changes of temperature and the conveyor mat is built up from modules manufactured from a material having a relatively great coefficient of thermal expansion, such as plastic.
The above problems play a role in particular when a wide conveyor mat built up from plastic modules is subjected to substantial changes of temperature, as in the case where by means of such conveyor mat, products are pasteurized in a pasteurizer. In a usual pasteurizer, products are slowly conveyed over a conveying track by means of a conveyor mat, while the temperature of the products is gradually increased to at least 80.degree. C. in order to kill bacteria present in the products. The conveyor mat has a width that may run up to more than 5 m and a length that may run up to more than 40 m. The great width of the conveyor mat, the substantial changes in temperature and the great coefficient of thermal expansion of plastic (about 0.15 mm/m/.degree. C.), much greater than that of the stainless steel from which the frame of a pasteurizer is made, render the above-mentioned guide construction unsuitable for this application. Instead, the conveying track must be of an extra wide design and be arranged in a very flat position. For the sake of safety, guide blocks are provided adjacent the lateral edges of the conveying track. Such a construction leads to high extra costs and substantial loss of space. Moreover, because of the length of a pasteurizer, sometimes more than 40 m, the lateral guides cannot be made from one piece, which may cause an uneven transition. Finally, pasteurizers are completely inaccessible during operation, so that dragging or jamming of a mat can only be detected on be basis of damages to the mat; at that point, however, it is already too late to take measures to "save" the mat.